It has long been known that tires for various vehicles, although worn smooth as a result of extended operation on abrasive road surfaces, nonetheless retain significant amounts of rubber on their circumferential surfaces so that new tread patterns may be cut or "grooved" into such surfaces, thereby allowing the tires to be returned to service and their operable lives extended for thousands of additional miles. Grooving of tires has been particularly prevalent in the trucking industry, where tractor/trailer vehicles can have up to 18 large tires, each of which costs several hundred dollars when purchased new. Obviously, a grooving technique that allows such tires to be rejuvenated so that their operable lives are significantly extended has found great favor with tractor/trailer owners and operators.
Previous tire groovers most often have operated by means of a heated cutting blade that slices through the rubber material on the circumferential surface of the tire being grooved. Such known tire groovers are discussed and referenced in U.S. Pat. No. 4,797,999, to Van Alstine, which is hereby incorporated in its entirety herein by reference. Known tire groovers have typically employed a sliding block or similar surface positioned completely behind or between the legs of a U-shaped cutting blade for guiding or steadying the tire groover along the circumference of the tire during grooving operations. In such tire groovers a sliding block or surface is always placed either rearward of the cutting edge of the blade or between the legs of the U-shaped blade, so that the sliding block or surface typically rides above a freshly cut portion of tire material which is squeezed or pinched between the blade legs and sliding block during tire grooving operations.
It is difficult to accurately control the movement of known tire groovers, because such known tire groovers tended to rock about the circumferential surface of a tire being grooved. Such rocking typically results in the creation of a groove having an uneven and imprecise depth. In known tire groovers, the operator's hand or hands, which provide the cutting force to the tool, is positioned above the cutting plane of the blade. When the operator applies cutting pressure the tool tends to rock forward with the blade acting as a pivot point. When the tool rocks forward increased friction is created at the front of the tool because the blade becomes angled or biased and is thereby pulled into the rubber. At this point, the tool typically begins to ride only on its front corner. As the tool continues to be pulled into the rubber by virtue of the angular orientation of the blade, any forward force exerted by the operator tends to jam the tool into the rubber. If the operator rocks the tool back to correct for this effect, he can easily bias the blade to cut out of the rubber thereby reducing the cutting depth. If he rocks the tool forward as a correction for this, he again creates the jamming effect at the front of the tool. Since the sliding block is free to rock about the rounded tire surface, the feel for the correct cutting angle is extremely vague and there is no way for an operator to "lock" the blade at a proper working angle. The result is a groove having an inconsistent depth.
During operation of known tire groovers, tire material immediately following the cutting blade is often trapped snugly between the blade sides and the sliding block or surface of the tool. As the cut is made, this trapped rubber must be squeezed (almost extruded) through the opening formed by the blade sides and the sliding block. The friction from this squeezing effect produces the need for more force from the operator to make a cut and also gives the cutting resistance of the tool a variable feel. In addition, known tire groovers tend to rock about the tire surface during operation. As the tool rocks, the cutting angle of the blade varies, sometimes pulling the tool towards and other times pushing it away from the tire surface. From this action, the sliding block of the tool is constantly making and breaking contact with the tire surface. As the sliding block comes in and out of contact with the tire surface, the variable feel of the cutting resistance is further aggravated.
In known tire groovers, the cutting blade and the sliding block or surface are fixed in space with respect to each other so that a change in position of the sliding block is immediately reflected by a corresponding change in the position of the cutting blade. During tire grooving, tire material immediately following the cutting edge of the blade is typically pinched or raised. This occurs because, at the point of the cut, the cutting blade which has its own thickness is interposed between the tire itself and the portion of tire material lying above the blade, which portion is cut away. Since this cut away portion of tire material is not immediately removed at the time of the cut, but instead remains in a tire groove for a short time thereafter, the sliding block or surface must ride above or along a pinched or raised surface during cutting.
When the sliding block or surface is caused to rise as a result of pinched or raised tire material, a corresponding change in the position and typically the height of the cutting blade occurs. This change in blade position causes a corresponding change or variation in the depth of the cut made by the tire grooving mechanism. Since the degree to which tire material is pinched or raised during cutting is typically not uniform, a groove having an uneven and imprecise depth often results. Moreover, the pinching or squeezing effect tends to increase friction between the sliding block and the tire surface creating a variable feel to the cutting resistance. This variable feel makes it difficult for an operator to properly control the tool during operation. In the past, rollers have been substituted for the sliding block in order to minimize friction between the tool and the tire surface. However, such rollers tend to give an uneven or imprecise cut because they allow the tool to rock about the tire surface.
It was found that the tire material which is pinched or raised during cutting, as well as the rearward positioning itself of the sliding surface, caused general difficulties in guiding or steadying the tire grooving mechanism during operations. It was further found that this pinching effect was a problem when cutting across a tire side or across already existing grooves. When beginning to cut at an existing groove but not in the same direction as that groove, the front edge of the cut rubber, now raised because the blade is passing under it, can catch against the front edge of a sliding block and completely stop the forward movement of the tool. This same problem occurs when the cut is started on the side of the tire.
In push type tire groovers, the sliding surface which should be in contact with the tire surface is typically blocked visually from the operator. Without the proper visual orientation, it is difficult for an operator to confirm that the tool is at a proper angle or depth.
It is an object of this invention to provide a stabile and precise mechanism for guiding and controlling the movement of a head member for a resistance-heated tire groover that greatly facilitates the accurate movement of a head member along the circumferential surface of a subject tire.
It is a further object of this invention to eliminate inaccuracies in groove depth caused by pinched or raised tire material.
It is a further object of this invention to eliminate the squeezing of cut rubber between the blade legs and the sliding surface of a tire groover.
These and other objects of the invention will be better appreciated after reading the succeeding description of the invention in conjunction with the accompanying drawings.